The primary objective is to advance our knowledge of lipid metabolism and atherosclerosis using animal models. A major area is the role of 12/15-lipoxygenase (LO) in atherosclerosis. 12/l5LOs are lipid-peroxidizing enzymes that oxygenate polyenoic fatty acids to their corresponding hydroperoxy derivatives. 12/15LOs have proatherogenic properties via their capacity to oxidize LDL, as well as antiatherogenic activities via their predominantly anti-inflammatory action. We previously showed that macrophage-specific 15LO overexpression in rabbits protects against atherosclerosis. In pilot experiments we found that, compared to 12/15LO+/+ apoE-/- mice, 12/15LO-/- apoE-/- mice are protected against atherosclerosis, a finding that is at variance with that of. A major goal of this application is to examine the biochemical milieu associated with 12/15LO expression that may underlie the divergent effects of the enzyme on atherosclerosis. Another major area is the role of intracellular lipolysis in lipid homeostasis. We produced perilipin (plin) knockout mice that displayed constitutional activated lipolysis. Perilipin is a major adipose lipid droplet protein that regulates the activity of hormone-sensitive lipase. Plin-/- mice were lean and resistant to diet-induced obesity. Breeding the plin-/- alleles into ob/ob and db/db mice reversed their obesity phenotype. Interestingly, ruptured atherosclerotic plaques in humans and advanced plaques of apoE-/- mice expressed perilipin. We will investigate the role of 12/15LO and perilipin with 5 specific aims. In the first 2 aims, we will study atherosclerosis development in 12/15LO-/- apoE-/- and 12/15LO+/+ apoE-/- mice, and, identify and quantify the eicosanoids and other metabolites in the atherosclerotic aortas from the 2 genotypes. In aims 3 and 4, to obtain mechanistic insight into the obesity-resistant phenotype of plin-/- mice, we will perform biochemical and molecular characterization as well as in vivo stable isotope and energy expenditure experiments on plin+/+ and plin-/- mice with and without ob/ob or db/db background. The creation of non-obese ob/ob and db/db mice (i.e., those that also inherited the plin-/- alleles) provides a unique opportunity to study the role of leptin in lipid and carbohydrate homeostasis in the presence and absence of obesity. Since perilipin, a lipid droplet-associated protein, is expressed in atherosclerotic lesions, in the last aim and in collaboration with we will compare the atherosclerosis susceptibility and plaque morphology of plin-/- and plin+/+ mice bred into apoE-/- and LDLR-/- background. We believe that the mechanistic experiments proposed will advance our understanding of lipid and carbohydrate metabolism, energy homeostasis, and atherosclerosis.